The overall aim of this research project is to seek a better understanding of the acoustic and perceptual basis of phonetic features and segments used in spoken language and how they are analyzed by the nervous system during the earliest stages of speech perception. The specific objectives of this work have focused on the perception of speech-like acoustic signals, perceptual development of speech processing abilities in infants, and the role of environmental experience in the form of laboratory training techniques on the reacquisition and selective modification of phonetic contrasts in mature adult listeners. From this program of research we hope to be able to distinguish between perceptual processes that are common to the general auditory system and those that may well require the postulation of specialized neural or perceptual mechanisms for processing speech signals.